1. Field of the Invention
The present invention relates in general to an electrochromic device having two thin glass elements and a free-standing gel, and more particularly, to a lightweight electrochromic device having a free-standing gel that cooperatively interacts with two thin glass elements to form a thick, strong unitary member which is resistant to flexing, warping, bowing, shattering and/or scattering.
2. Background Art
Heretofore, various automatic rearview mirrors for motor vehicles have been devised which automatically change from the full reflectance (day) mode to the partial reflectance (night) mode(s) for glare protection purposes from light emanating from the headlights of vehicles approaching from the rear. The electrochromic mirrors disclosed in U.S. Pat. No. 4,902,108, entitled xe2x80x9cSingle-Compartment, Self-Erasing, Solution-Phase Electrochromic Devices Solutions for Use Therein, and Uses Thereofxe2x80x9d, issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No. 1,300,945, entitled xe2x80x9cAutomatic Rearview Mirror System for Automotive Vehiclesxe2x80x9d, issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No. 5,128,799, entitled xe2x80x9cVariable Reflectance Motor Vehicle Mirrorxe2x80x9d, issued Jul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled xe2x80x9cElectro-Optic Devicexe2x80x9d, issued Apr. 13, 1993, to H. J. Byker et al.; U.S. Pat. No. 5,204,778, entitled xe2x80x9cControl System For Automatic Rearview Mirrorsxe2x80x9d, issued Apr. 20, 1993 to J. H. Bechtel; U.S. Pat. No. 5,278,693, entitled xe2x80x9cTinted Solution-Phase Electrochromic Mirrorsxe2x80x9d, issued Jan. 11, 1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380, entitled xe2x80x9cUV-Stabilized Compositions and Methodsxe2x80x9d, issued Jan. 18, 1994, to H. J. Byker; U.S. Pat. No. 5,282,077, entitled xe2x80x9cVariable Reflectance Mirrorxe2x80x9d, issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376, entitled xe2x80x9cBipyridinium Salt Solutionsxe2x80x9d, issued Mar. 15, 1994, to H. J. Byker; U.S. Pat. No. 5,336,448, entitled xe2x80x9cElectrochromic Devices with Bipyridinium Salt Solutionsxe2x80x9d, issued Aug. 9, 1994, to H. J. Byker; U.S. Pat. No. 5,434,407, entitled xe2x80x9cAutomatic Rearview Mirror Incorporating Light Pipexe2x80x9d, issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No. 5,448,397, entitled xe2x80x9cOutside Automatic Rearview Mirror for Automotive Vehiclesxe2x80x9d, issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No. 5,451,822, entitled xe2x80x9cElectronic Control Systemxe2x80x9d, issued Sep. 19, 1995, to J. H. Bechtel et al., each of which patents is assigned to the assignee of the present invention and the disclosures of each of which are hereby incorporated herein by reference, are typical of modern day automatic rearview mirrors for motor vehicles. Such electrochromic mirrors may be utilized in a fully integrated inside/outside rearview mirror system or as an inside or an outside rearview mirror system. In general, in automatic rearview mirrors of the types disclosed in the above-referenced U.S. Patents, both the inside and the outside rearview mirrors are comprised of a relatively thin electrochromic medium sandwiched and sealed between two glass elements.
In most cases, when the electrochromic medium which functions as the media of variable transmittance in the mirrors is electrically energized, it darkens and begins to absorb light, and the more light the electrochromic medium absorbs the darker or lower in reflectance the mirror becomes. When the electrical voltage is decreased to zero, the mirror returns to its clear or substantially clear high reflectance state. In general, the electrochromic medium sandwiched and sealed between the two glass elements is comprised of solution-phase, self-erasing system of electrochromic materials, although other electrochromic media may be utilized, including an approach wherein a tungsten oxide electrochromic layer is coated on one electrode with a solution containing a redox active material to provide the counter electrode reaction. When operated automatically, the rearview mirrors of the indicated character generally incorporate light-sensing electronic circuitry which is effective to change the mirrors to the dimmed reflectance modes when glare is detected, the sandwiched electrochromic medium being activated and the mirror being dimmed in proportion to the amount of glare that is detected. As glare subsides, the mirror automatically returns to its normal high reflectance state without any action being required on the part of the driver of the vehicle.
The electrochromic medium is disposed in a sealed chamber defined by a transparent front glass element, a peripheral edge seal, and a rear mirror element having a reflective layer, the electrochromic medium filling the chamber. Conductive layers are provided on the inside of the front and rear glass elements, the conductive layer on the front glass element being transparent while the conductive layer on the rear glass element may be transparent or the conductive layer on the rear glass element may be semi-transparent or opaque and may also have reflective characteristics and function as the reflective layer for the mirror assembly. The conductive layers on both the front glass element and the rear glass element are connected to electronic circuitry which is effective to electrically energize the electrochromic medium to switch the mirror to nighttime, decreased reflectance modes when glare is detected and thereafter allow the mirror to return to the daytime, high reflectance mode when the glare subsides as described in detail in the aforementioned U.S. Patents. For clarity of description of such a structure, the front surface of the front glass element is sometimes referred to as the first surface, and the inside surface of the front glass element is sometimes referred to as the second surface. The inside surface of the rear glass element is sometimes referred to as the third surface, and the back surface of the rear glass element is sometimes referred to as the fourth surface.
Recently, electrochromic mirrors have become common on the outside of vehicles, and suffer from the fact that they are significantly heavier than standard outside mirrors. This increased weight with electrochromic mirrors exerts a strain on the mechanisms used to automatically adjust the position of the outside mirrors. One method of decreasing the weight of an electrochromic mirror is by reducing the thickness of both glass elements or even remove one glass plate. For example, in solid state electrochromic devices, such as those described in U.S. Pat. No 4,973,141 to Baucke et al., where all the components comprise solid state elements, e.g., solid state electrochromic layers (WO3 and MoO3), solid, hydrogen ion-conducting layers, etc., it has been proposed that the back plate is optional. This is possible because the other layers are all in the solid phase and remain attached to the front plate. In electrochromic devices containing at least one solution-phase electrochromic material on the other hand, it is not possible to remove one glass plate because the solvent and electrochromic material would leak out. Therefore, the only option for electrochromic devices containing a solution is to decrease the glass thickness. Unfortunately, as the thickness is decreased the individual glass elements become fragile and flexible and remain that way during and after the manufacture of an electrochromic mirror. This is especially true as the mirrors become larger such as is needed on vehicles like sport-utility vehicles and very large trucks, e.g., tractor-trailers. It is therefore difficult to produce a commercially desirable electrochromic mirror containing at least one solution-phase electrochromic material that has two thin glass elements because each thin glass element will be much more likely to flex, warp, bow and/or shatter. Properties of a solution-phase electrochromic device, such as coloring and clearing times and optical density when colored, are dependent on the thickness of the electrochromic layer (e.g., the spacing between the two glass elements). Maintaining uniform spacing is necessary to maintain uniform appearance. The spacing between thin glass elements can be easily changed even after device manufacture by applying subtle pressure on one of the glass plates. This creates an undesirable non-uniformity in the appearance of the device.
Consequently, it is desirable to provide an improved electrochromic device, such as an electrochromic mirror, window, etc, having a free-standing gel containing at least one solution-phase electrochromic material, where the gel cooperatively interacts with two thin glass elements to form a thick, strong unitary member which is resistant to flexing, warping, bowing, shattering and/or scattering and helps maintain uniform spacing between the thin glass elements.
Accordingly, a primary object of the present invention is to provide a lightweight electrochromic device having a free-standing gel containing at least one solution-phase electrochromic material, where the gel cooperatively interacts with two thin glass elements to form a thick, strong unitary member which is resistant to flexing, warping, bowing, shattering and/or scattering.
Another object of the present invention is to provide a lightweight electrochromic device having two thin glass elements that exhibits reduced vibration, distortion and double imaging.
The above and other objects, which will become apparent from the specification as a whole, including the drawings, are accomplished in accordance with the present invention by providing an electrochromic device with thin front and rear spaced glass elements. A layer of transparent conductive material may be placed onto the second surface, and either another layer of transparent conductive material or a combined reflector/electrode may be placed onto the third surface. A chamber is defined by the layers on the interior surfaces of the front and rear glass elements and a peripheral sealing member. In accordance with the present invention, the chamber contains a free-standing gel comprising a solvent and a crosslinked polymer matrix, and further contains at least one electrochromic material in solution with the solvent and interspersed in the crosslinked polymer matrix, where the gel cooperatively interacts with the thin glass elements to form a thick, strong unitary member which is resistant to flexing, warping, bowing, shattering and/or scattering, and further allows the mirror to exhibit reduced vibration, distortion and double imaging.